Control method for dual dependent variable CAM timing system

Abstract

In a dual dependent variable cam timing system, the desired intake global phase is reached by directly controlling the global phase of exhaust VCT phaser and controlling the local phase of intake VCT phaser. The global intake set point specified by an engine controller is converted into a local intake set point first, then passed through a set point filter, and compared with the measured local intake phase. The difference (error signal) is passed through a PI controller and a phase compensator, which have the same control structures as those of exhaust VCT phaser control, to form a control signal.

What is claimed is:  
     
       1. A variable cam timing (VCT) control system used in an internal combustion engine, said system having a dual dependent cam shaft configuration, wherein an intake cam shaft is dependent upon an exhaust cam shaft, comprising: 
       a) an exhaust phaser engaging said exhaust cam shaft;  
       b) an intake phaser engaging said intake cam shaft, the movement of said intake cam shaft being dependent upon the movement of said exhaust cam shaft;  
       c) a first feedback loop for correcting errors relating to said intake phaser, said first feedback loop including a measured intake phase signal, being used to compare with a local intake set point and being used to generate an error signal used by the first feedback loop; and  
       d) a second feedback loop for correcting errors relating to said exhaust phaser, said second feedback loop including a measured exhaust phase signal, wherein said measured exhaust phaser signal is used for adjustments of both said exhaust phaser and said intake phaser.  
     
     
       2. The system of  claim 1 , wherein said error signal is used by a control law to generate a first control signal. 
     
     
       3. The system of  claim 2 , wherein said measured exhaust phase signal is used to compare with an exhaust setpoint and generate an error signal that is used by said control law to generate a second control signal. 
     
     
       4. The system of  claim 3 , wherein said second control signal is also used to compare with said global intake set point to generate said local intake setpoint. 
     
     
       5. The system of  claim 1 , further comprising a controller for controlling inputs to both the first feedback loop and the second feedback loop. 
     
     
       6. The system of  claim 1 , further comprising a crankshaft coupled with said exhaust cam shaft. 
     
     
       7. The system of  claim 6 , further comprising coupling means for coupling said exhaust cam shaft to said crank shaft by a first coupling meanings. 
     
     
       8. The system of  claim 1 , further comprising coupling means for coupling said exhaust cam shaft to said intake cam shaft by a second coupling means. 
     
     
       9. In a variable cam timing (VCT) control system used in an internal combustion engine, said system having a dual dependent cam shaft configuration, wherein an intake cam shaft is dependent upon an exhaust cam shaft, a method comprising the steps of: 
       providing an exhaust phaser engaging said exhaust cam shaft;  
       providing an intake phaser engaging said intake cam shaft, the movement of said intake cam shaft being dependent upon the movement of said exhaust cam shaft;  
       providing a first feedback loop for correcting errors relating to said intake phaser, said first feedback loop including a measured intake phase signal, being used to compare with a local intake set point and being used to generate an error signal used by the first feedback loop;  
       providing a second feedback loop for correcting errors relating to said exhaust phaser, said second feedback loop including a measured exhaust phase signal; and  
       using said measured exhaust phase signal, correcting both a global intake set point and an exhaust set point, thereby providing a more accurate correction to said dual dependent variable cam timing system.  
     
     
       10. The method of  claim 9 , wherein the error signal is used by a control law to generate a first control signal. 
     
     
       11. The method of  claim 10 , wherein said measured exhaust phase signal is used to compare with an exhaust setpoint and generate said error signal that is used by said control law to generate a second control signal. 
     
     
       12. The method of  claim 11 , wherein said second control signal is also used to compare with said global intake set point to generate said local intake setpoint. 
     
     
       13. The method of  claim 9  further comprising controlling inputs to both the first feedback loop and the second feedback loop using a controller. 
     
     
       14. The method of  claim 9  further comprising coupling said exhaust cam shaft with a crank shaft by a first coupling means. 
     
     
       15. The method of  claim 9  further comprising coupling said exhaust cam shaft with said intake cam shaft by a second coupling means.